Various types of engineered wood composites, such as flakeboard, waferboard, particle board, and strand board are known and used in construction applications. Strand board, particularly oriented strand board, has enjoyed success as a building material since its introduction to market in approximately 1981. Such composite products which are made from lignocellulosic materials include “composite boards”, which include oriented strand board (OSB), wafer board, straw board, fiber board, chip board and particle board. The board substrate can be prepared by applying an adhesive to lignocellulosic particles, chips or fibers, specifically wood particles, wood chips and lignocellulosic particles, and subsequently forming the lignocellulosic material into the desired board through application of heat and pressure.
Oriented strand board is produced from secondary wood material that is reduced to flat strands, which are then reconsolidated into durable panels of high mechanical properties. Production of oriented strand board and other wood composites requires the creation of durable bonds between and among the flat strands using synthetic adhesives, waxes or modifiers as well as a considerable amount of effort and energy to bond the particles together and provide high mechanical properties, strength, dimensional stability, and durability. This is accomplished in conventional practice though mixing of strands and adhesives and application of heat and pressure to form the board.
Small variations in the process parameters of the binding protocol may greatly affect properties of the end product strand board. Additionally, small improvements and innovation in the area of oriented strand board may lead to significant production cost savings, improved process efficiency and safety, as well as the manufacture of improved products.
In the conventional practice used in the manufacture of oriented strand board, resin, which acts as an adhesive is sprayed on flat strands in revolving blenders through conventional nozzles. The resin acts as a waterproofing and adhesive component. Small amounts of wax, which may be in emulsion form (generally about 1.5% by weight or less on a solids basis) are used as well. Resin droplets are atomized into the strand board components during manufacture in a conventional manner using a spinning disk sprayer.
Adhesives currently used in the manufacturer of various wood composite products include urea-formaldehyde, phenol-formaldehyde, melamine-urea-formaldehyde, melamine-formaldehyde resins, and certain isocyanate polymers. Examples of resins which are used in the art of oriented strand board manufacture include phenyl formaldehyde (novolaks and resoles) and poly(diphenylmethane diisocyanate) (pMDI). The resin is applied first and the wax emulsion applied separately.
Commercial wax emulsions used in the oriented strand board industry are known to include slack wax and fatty acid soaps and non-ionic emulsifiers. One commercially used example includes Cascowax EW-58A from Borden Chemicals. Generally, due to lack of compatibility between prior wax emulsions and the resins used, such prior art wax emulsions based on fatty acid and base emulsifiers separate into wax and water when mixed with either type of resin usually causing plugging of lines, requiring separate application. One prior emulsion prepared by Mobil Oil based on a complex blend of emulsifiers, demonstrated compatibility with phenol formaldehyde, but was expensive for oriented strand board production.
In manufacturing oriented strand board there are several key properties necessary to achieve acceptable properties, including low edge swell and water absorption as well as strong internal bond strength and good flexural stiffness and flexural strength.
There exists a need in the art for a manufacturing process and/or composition for forming composite wood panels, such as oriented strand board, that is comparable to properties achieved by prior wax emulsions used in the art and/or improves upon such properties, while lowering the cost of manufacture and preferably also simplifying the application of resins and wax emulsions in the composite board manufacturing procedure.